Second harmonic generation in a laser channel

Abstract

An intense laser beam guided through a low-density plasma channel produces second harmonic emission that leaks out in the high-density outer region, propagating in a low-angle hollow cone with respect to channel axis. For a channel with interior density 0.25$n_{\rm cr}$, outer region density 0.64$n_{\rm cr}$ ($n_{\rm cr}$ being the critical density), laser wavelength 1 $\mu$ and channel radius ${\sim}5~\mu$m, the angle $\theta$ of the cone ${\sim}19^{\circ}$. The second harmonic power shows an oscillatory behavior with the density of the channel. It peaks at certain densities of the plasma channel. The heights of the peaks of second harmonic power are higher at greater densities.